Retractable Underreamer

ABSTRACT

An underreamer is provided in which the cutting elements are retracted into the tool body during run in, extensible for the performance of cutting operations, and retractable into the body of the tool afterwards.

FIELD OF THE INVENTION

The invention relates to tools used in underreaming well bores, providing a underreaming tool with radially extendable and retractable cutting elements.

BACKGROUND OF THE INVENTION

Underreaming of a well bore is a means of expanding a zone in a well bore to a greater diameter by cutting material away from the side of the well bore. Because the well bore is to be expanded in diameter, it is necessary to provide a tool that can run into the well bore in a “closed” position, then allow the cutting elements of the tool to extend radially outward until the desired bore diameter is reached.

An example of such a tool is described in U.S. Pat. No. 4,282,942 to Longmore. That tool utilizes reverse circulation pressure to drive a cam to pivotally extend the cutting elements. Once the underreaming operation is complete, the reverse circulation pressure is removed and the cutting elements are allowed to collapse back to the tool body by gravity.

Another type of underreamer is described in U.S. Pat. No. 5,853,054 to MaGarian, et al. That tool utilizes hydraulic pistons to pivotally extend and retract the cutting elements of the tool. However, it also anticipates that power to these pistons may be lost, and provides for biasing springs to retract the cutting elements if power is lost to the retracting piston.

While useful, underreaming tools create a risk of having the tool stuck downhole if the cutting elements do not sufficiently or fully retract. Because underreamers are used to selectively increase the diameter of well bores, the nature of the operation will create a shoulder above the underreamed zone where the well bore narrows to its original diameter. Conversely, if the underreaming operation is performed below casing, the casing itself will present a narrow diameter through which the tool must fit to be retrieved from the well bore. Thus, an underreamer that fails to fully retract may become stuck, requiring time consuming efforts (and therefore expensive) efforts to fish it out of the well bore, or to grind through it.

Other reliability problems can occur with current underreamers. For example, the cutting elements may fail to fully extend, preventing the underreaming operation from proceeding to the full desired diameter. Such a circumstance may require retrieving the underreamer from the well bore, repairing or replacing it, and running into the well bore again to complete the underreaming operation. Such instances are extremely undesirable due to the lost time and expense of running in and out of the well bore.

Accordingly, it is an object of the invention to provide an underreamer with improved reliability. Further objects of the invention include further improving reliability by providing a positive indication at the surface when the cutting elements have been fully extended, and again when they have been fully retracted.

SUMMARY OF THE INVENTION

The invention is an underreamer comprising a cam-driven mechanism to extend and retract the cutting elements. When activated, the cam applies a radial force to the cutting elements essentially perpendicular to the longitudinal axis of the tool body. Thus, the cutting elements do not pivot relative to the tool body as they extend and retract, but move radially essentially perpendicularly to the longitudinal axis of the tool.

The invention further provides a mechanism for selectively setting the cam in position to extend the cutting elements, and for selectively setting the cam in position to retract the cutting elements after underreaming operations are complete. This mechanism provides two different drop ball seats, the lower one of smaller diameter than the upper one. (As used herein, “upper” is intended to mean only “closer to the surface,” because the tool string may not be vertical.)

When it is desired to set the cutting elements in the extended position, a first drop ball of a diameter small enough to pass through the upper drop ball seat is dropped through the tool string. The first drop ball travels though the tool body, past the upper drop ball seat, and seats in the lower drop ball seat, interrupting fluid flow through the tool body. Hydraulic pressure can then be used to shear a first set of shear screws. When the first set of shear screws shear, the hydraulic pressure shifts the cam and lower ball seat downward, moving the cutting elements into their extended position. Once the cutting elements are fully extended, a lower flow diverter opens to allow fluid flow around the lower ball seat. The resulting reduction in hydraulic pressure provides a positive indication at the surface that the cutting elements are fully extended.

Similarly, when the underreaming operation is complete and it is desired to set the cutting elements in the retracted position, a second drop ball of a diameter sufficient to seat in the upper drop ball seat is dropped through the tool string. The second drop ball seats in the upper drop ball seat, again interrupting fluid flow through the tool body. Hydraulic pressure can then be used to shear a second set of shear screws. When the second set of shear screws shear, the hydraulic pressure shifts the cam and upper ball seat downward, moving the cutting elements into their retracted position. Once the cutting elements are fully retracted, an upper flow diverter opens to allow fluid flow around the upper ball seat. The resulting reduction in hydraulic pressure provides a positive indication at the surface that the cutting elements are fully retracted.

In a preferred embodiment, upper and lower ratcheting followers are provided, so that as each shift of the cam is performed, the ratcheting followers prevent reverse shifting of the cam.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of one embodiment of the underreamer of the present invention in the run-in position.

FIG. 1A is an expanded cross-sectional view of section A-A′ of FIG. 1.

FIG. 1B is an expanded cross-sectional view of section B-B′ of FIG. 1.

FIG. 2 is a cross-sectional view of one embodiment of the underreamer of the present invention with the cutting elements in the extended position.

FIG. 2A is an expanded cross-sectional view of section C-C′ of FIG. 2.

FIG. 2B is an expanded cross-sectional view of section D-D′ of FIG. 2, reflecting the position of the lower ball seat before circulation resumes.

FIG. 2C is an expanded cross-sectional view of section D-D′ of FIG. 2, reflecting the position of the lower ball seat after circulation resumes.

FIG. 3 is a cross-sectional view of one embodiment of the underreamer of the present invention with the cutting elements in the retracted position.

FIG. 3A is an expanded cross-sectional view of section E-E′ of FIG. 3, reflecting the position of the upper ball seat before circulation resumes.

FIG. 3B is an expanded cross-sectional view of section F-F′ of FIG. 3.

FIG. 3C is an expanded cross-sectional view of section E-E′ of FIG. 3, reflecting the position of the upper ball seat after circulation resumes.

FIG. 3D is an expanded cross-sectional view of section G-G′ of FIG. 3C, provided to show greater detail.

FIG. 4A is a cross-sectional view of an embodiment of the cam section of an underreamer assembly during the process of extending the cutting elements in accordance with the present invention.

FIG. 4B is a cross-sectional view of an embodiment of the cam section of an underreamer assembly during the process of retracting the cutting elements in accordance with the present invention.

FIG. 5 is a perspective view of an embodiment of an underreamer assembly in accordance with the present invention.

FIG. 6 is a perspective view of an embodiment of a cutting element of the present invention.

DETAILED DESCRIPTION

Referring to FIGS. 1-3, cross-sectional views of an embodiment of an underreamer of the present invention are shown, showing the tool positioned for run-in (FIGS. 1, 1A, 1B), with the cutting elements extended (FIGS. 2, 2A, 2B, 2C), and with the cutting elements retracted for tool retrieval (FIGS. 3, 3A, 3B, 3C, 3D).

Underreamer 10 comprises a tool body 12, cam 14, cutting elements 16, upper ball seat 18, and lower ball seat 20. Cutting elements 16 are aligned with openings 22 in tool body 12 (see also tool body 512 with openings 522 of FIG. 5). Tapers 24 of cam 14 are preferably offset differently from their respective cutting elements 16, so that when the cam 14 is shifted to displace cutting elements 16, cutting elements 16 will not all shift at once, decreasing the amount of force necessary and reducing the strain on the tool.

A more detailed view of this activation timing is shown in FIGS. 4A and 4B. As shown in FIG. 4A, when cam 14 is being shifted downward to extend cutting elements 16A, 16B, 16C, and 16D, the cam 14 engages these cutting elements with second leading edge 24B′ of second taper 24B, third leading edge 24C′ of third taper 24C, fourth leading edge 24D′ of fourth taper 24D, and fifth leading edge 24E′ of fifth taper 24E, respectively. As reflected in FIG. 4A, cam 14 is preferably designed so that these leading edges first engage their respective cutting elements at different times.

Similarly, FIG. 4B provides a detailed view of cam 14 as it is being shifted downward to retract cutting elements 16A, 16B, 16C, and 16D. In this case, cam 14 engages these cutting elements with first leading edge 24A′ of first taper 24A, second leading edge 24B′ of second taper 24B, third leading edge 24C′ of third taper 24C, and fourth leading edge 24D′ of fourth taper 24D, respectively. Again, cam 14 is preferably designed so that these leading edges first engage their respective cutting elements at different times.

Referring again to FIGS. 1-3, those of skill in the art will recognize that the number and size of cutting elements 16 (and thus the number and size of tapers 24 and openings 22) is a matter of design choice, and may vary in accordance with the requirements of particular downhole environments. Additionally, one or more of cutting elements 16 may be replaced with a stabilizing element (not shown) that would open and close in the same manner as the cutting elements 16, but would not provide any effective cutting action during underreaming. Rather such a stabilizing element would serve to stabilize the underreamer 10 while in operation.

Once the underreamer 10 is positioned in a well bore (not shown) the cutting elements 16 must be opened to allow underreaming to begin. Referring more particularly to FIGS. 2, 2A, 2B, and 2C, a first drop ball 26 is circulated or allowed to fall to the underreamer 10. First drop ball 26 is of sufficiently small diameter that it passes through upper ball seat 18. (Upper ball seat 18 is of larger diameter than lower ball seat 20). First drop ball 26 continues through underreamer 10 until it seats on lower ball seat 20, arresting fluid flow through underreamer 10.

Those of skill in the art will recognize that, while the use of ball seats and drop balls is embodied in the preferred embodiment of the invention, any seat capable of engaging a plugging device may be used in place of the ball seats described herein, and other plugging devices known to those of skill in the art may be used in place of drop balls.

The increasing hydraulic pressure forces shears first lower shear screws 28, allowing piston 19 to shift downward. This action causes first upper shear screws 62 to shear and releases lower ball seat 20, lower seal sleeve 30, cam 14, and upper ball seat 18 to travel downward until lower seal sleeve 30 engages lower shoulder 32. This displacement aligns the tapers 24 of cam 14 with cutting elements 16 so that cutting elements 16 are extended from the tool body 12. This motion also moves upper retaining ring 66 into contact with upper shoulder 68.

During the course of the opening operation, upper ratchet 94 travels downward along upper ratchet platen 96, providing a positive locking force prevent upward movement of piston 19.

Referring to FIG. 2C, this downward displacement also moves lower locking balls 36 into a position where they are aligned with a lower ball release taper 35 in lower intermediate sleeve 34. Lower locking balls 36 originally seated through lower sealing sleeve ball slots 31 into grooves 37 in lower ball seat 20. With lower locking balls 36 allowed to move outward, lower ball seat 20 is forced downward until lower ball seat bypass ports 38 align with lower sealing sleeve bypass ports 40. This alignment allows fluid to flow around first drop ball 26, providing a positive pressure indication to the surface that cutting elements 16 are in the extended position.

As part of the setting process, lower ratchet 42 (see FIGS. 2B and 2C) travels down-ward along lower ratchet platten 44, providing a positive lock preventing lower sealing sleeve 30 and lower ball seat 20 from shifting upwards.

When underreaming is complete, it is necessary to retract cutting elements 16 to allow retrieval of underreamer 10. Referring to FIGS. 3, 3A, 3B, and 3C, second drop ball 46 is circulated or allowed to fall into underreamer 10 until it seats on upper ball seat 18. Once second drop ball 46 is seated, fluid flow through the underreamer 10 is stopped.

Fluid pressure shears second upper shear screws 70, upper ball seat 18 shift downward, allowing first upper locking balls 48 drop into upper ball seat grooves 52, locking upper ball seat 18 and upper sealing sleeve 50 together to close first gap 78. Continued downward movement of upper ball seat 18 forces first upper locking balls 48 outward by the curvature of upper ball seat grooves 52, releasing the lock between upper ball seat 18 and upper sealing sleeve 50.

Cam 14 can now move downward, shearing lower shear screws 54. The shearing of second lower shear screws 54 allows lower inner sleeve 56 (and therefore cam 14 and upper ball seat 18) to move relative to lower sealing sleeve 30 and lower ball seat 20. The down-ward shift of cam 14 draws cutting elements 16 inward to a fully retracted position.

Third upper shear screws 76 also shear in this action, releasing seal bushing 64 into annulus 92 to prevent fluid flow through annulus 92 when circulation is reestablished. Seal bushing 92 is allowed to “float” to equalize pressures above and below it.

Downward travel continues until lower retaining ring 67 engages inner shoulder 74. Hydraulic pressure shears fourth upper shear screws 77, allowing a continued downward shift of upper ball seat 18 and spacer 51. As reflected in FIGS. 3C and 3D, second upper locking balls 49 are now able to fall outward into lower retaining ring ball slots 69 due to the relative motion between spacer 51 and lower retaining ring 67.

Cam 14 is pushed downward until further movement is stopped by contact with intermediate shoulder 58.

Upper ball seat 18 and spacer 51 shift downward, closing second gap 80, until the lower end of spacer 51 shoulders on torn end 81 of bottom push tube 83. (See FIG. 3C). In this position, upper ball seat bypass ports 82 are aligned with upper sealing sleeve bypass ports 84. This alignment allows fluid to flow around second drop ball 46, providing a positive pressure indication to the surface that cutting elements 16 are in the retracted position.

Referring to FIG. 5, additional features of a preferred embodiment of the invention are shown. Underreamer 510 comprises tool body 512. Tool body 512 comprises a housing cover 524 that can be bolted in place through bolt holes 526, allowing easy field disassembly of the underreamer and allowing expendable parts, such as shear screws and cutting elements, to be replaced in the field so that the underreamer may be ready for immediate re-use. Those of skill in the art will recognize that housing cover 524 is not limited in shape or form to that depicted, but may vary in accordance with engineering choice. Housing cover 524 also preferably provides openings 522 allowing extension of cutting elements through the housing cap 524. Keys 528 fit into milled slots 530, 532 in tool body 512 and housing cover 524, respectively. These keys improve the torsional strength of the tool. Alternatively, either the tool body 512 or the housing cover 524 may be provided with key extensions, and slots milled only into the other part to receive the key extensions. As those of skill in the art will recognize, such key extensions may take a variety of shapes and sizes.

Referring to FIG. 6, a typical cutting element is shown. The cutting element 610 has a body 612 with an upper surface 614 and a lower surface 616 for engagement with the tapers of the cam. Cutters 618 provide the cutting action when cutting element 610 is extended from the underreamer.

The above examples are included for demonstration purposes only and not as limitations on the scope of the invention. Other variations in the construction of the invention may be made without departing from the spirit of the invention, and those of skill in the art will recognize that these descriptions are provide by way of example only. 

1. An underreamer for use in well bores, comprising a tool body, a selectively positional cam within said tool body, and a cutting element positional by said cam in a retracted position relative to said tool body, and also positional by said cam in an extended position relative to said tool body, wherein the motion of said cutting element relative to said tool body is essentially perpendicular to the longitudinal axis of said tool body.
 2. The underreamer of claim 1, wherein said cam is selectively positional to retain said cutting element in a retracted position during run in.
 3. The underreamer of claim 1, wherein said cam is selectively positional to retain said cutting element in an extended position during cutting operations.
 4. The underreamer of claim 1, wherein said cam is selectively positional to retain said cutting element in a retracted position after cutting operations are completed.
 5. The underreamer of claim 1, additionally comprising a seat capable of engaging a plugging device, wherein said seat obstructs fluid flow through the underreamer when a plugging device is engaged on said seat.
 6. The underreamer of claim 5, additionally comprising a flow diverter, wherein said flow diverter allows fluid flow around said seat when said cam positions said cutting element in an extended position.
 7. The underreamer of claim 5, additionally comprising a second seat capable of engaging a second plugging device, wherein said second seat obstructs fluid flow through the underreamer when a second plugging device is engaged on said second seat.
 8. The underreamer of claim 7, additionally comprising a second flow diverter, wherein said second flow diverter allows fluid flow around said second seat when said cam positions said cutting element in a retracted position.
 9. The underreamer of claim 1, additionally comprising a plurality of cutting elements positional by said cam in a retracted position, and also positional by said cam in an extended position.
 10. The underreamer of claim 1, additionally comprising a stabilizer element, wherein said stabilizer element may be extended and retracted in the same manner as said cutting element.
 11. The underreamer of claim 10, comprising a plurality of stabilizer elements.
 12. The underreamer of claim 1, wherein said tool body additionally comprises a housing cover, and wherein said housing cover is selectively detachable from the remainder of said tool body.
 13. The underreamer of claim 12, additionally comprising a key, wherein said key extends into said tool body and provides a positive positional lock between said tool body and said housing cover.
 14. The underreamer of claim 12, additionally comprising a key, wherein said key extends into said housing cover and provides a positive positional lock between said tool body and said housing cover.
 15. A method of performing an underreaming operation in a well bore, comprising the steps of running a tool body into position downhole with a cutting element retracted relative to said tool body, selectively positioning a cam within said tool body to extend said cutting element relative to said tool body by moving said cutting element in a direction essentially perpendicular to the longitudinal axis of said tool body, underreaming the wellbore, and selectively positioning said cam to retract said cutting element.
 16. The method of claim 15, additionally comprising the step of providing a pressure indication when the step of selectively positioning a cam within said tool body to extend said cutting element relative to said tool body is complete.
 17. The method of claim 15, additionally comprising the step of providing a pressure indication when the step of selectively positioning said cam to retract said cutting element is complete. 